The nation's top-selling annual flower — favored for its last-frost-to-first-frost profusion of colorful blooms — has been struck by a killer mildew that can be carried by the wind and lingers in the soil.

"Impatiens have been a sure thing for years and years," said Cornell plant pathologist Margery Daughtrey. "Now they are risky."

Found in just about every state east of the Mississippi and with no cure, impatiens downy mildew, which hides on the underside of the plant's leaves, has put growers and retailers in a tough spot: Take the vulnerable plant and big-time seller off the shelves to protect the unsuspecting customer from a disappointing garden experience? Or risk the ire of the customer for whom impatiens is the go-to shade bedding plant?

Gardeners of every stripe, from rank beginners and time-strapped homeowners to seasoned veterans, count on impatiens to bring a shady spot to life.

Kathy Metro, who has been gardening in Hampstead for 25 years, had no idea mildew was the reason her impatiens looked so bad last summer. She pulled them out early, thinking there was something wrong with her soil.

"It is my favorite flower. I love the colors," said Metro, who bought more than 100 last year in orange, red, pink and white. "They have such a pretty showing."

This year, she will try something different to brighten her shade gardens, she said. "I could take a chance, but to spend all that money and then have them die off?"

Meanwhile, some growers are making the decision on their own, cutting back the number of impatiens they grow by as much as half, or cutting out the plant altogether.

"While impatiens generate significant revenue in the spring, we want our customers to be successful in their gardening efforts and do not feel we can sell impatiens in good conscience," said Jay Meadows, president of Meadows Farms Nurseries and Landscape, which has 22 outlets in the Baltimore region. Impatiens represent a quarter of his company's bedding plant sales.

"We hope other garden centers and nursery supply companies will refrain from the temptation to sell impatiens," he said. "We feel they are doing their customers an injustice by selling this product until this very serious disease is under control."

But the disease can survive the winter in the soil. It loves cool, wet spring weather, and wind can carry the spores 100 miles or more. Even if you did not see evidence of the disease during the last growing season, that doesn't mean you are safe this year, experts say. It is in 32 states, including Maryland, and the District of Columbia.

Area garden centers seem split on the matter. Behnke's in Beltsville won't carry impatiens and neither will Valley View Farms in Cockeysville. But Homestead Gardens in Davidsonville will. Big-box stores like Home Depot, Lowes and Walmart will still carry them.

"Even though the growers can treat the plants with fungicides," said Marian Parsley of Behnke's, "that only lasts for a window of time, and right now there is no remedy available to the home gardener."

"I have been going around to garden clubs spreading the word," said Carrie Engel of Valley View, which sold a quarter of a million dollars worth of impatiens last year. "There is almost a relief. They had the problem last year and now they know it wasn't their fault.

"After that, the gardeners are like, OK, what else have you got?"

The answer may be begonias, another colorful bloomer for the shade. Growers like Gary Mangum of Bell Nursery in Burtonsville are putting their money there and in New Guinea impatiens, a cousin of the common impatiens and mildew-resistant.

It isn't easy for a grower to turn on a dime, but he cut the number of impatiens by half and increased the number of begonias he is growing.

"It is difficult in one short year to go in a completely different direction," he said. "But we want the consumer to have a good experience."

Mike Leubecker of Tidal Creek Growers, which supplies Homestead Gardens, is planting about 40 percent fewer impatiens, but the plants will be there for the determined customer — along with signs and banners to educate gardeners.